Reconditioning spark plugs



y 8, 1945. A. s. FRY ET AL 3 1 RECONDITIONING SPARK PLUGS Filed May 8,1943 ELL-'ICTE/C CONDUCTANCE TEMPE? 4 rues Enventors Q (IttornegsPatented May 8, .1945

RECONDITIONING SPARK PLUGS Arthur s. Fry and Lloyd 1.. Withrow, Detroit,

Mich., assignors to General Motors Corporation, Detroit, Mich., acorporation of Delaware Application May 8, 1943, Serial No. 486,200

9 Claims.

This invention has to do with reconditioning spark plugs.

Engine deposits from leaded gasolines afiect deleteriously theelectrical resistance of spark plug .insulators at high temperatures. Ithas been proposed heretofore to sand blast spark plugs in an effort toremove the leaded deposits from the porcelains and thus to minimize theeffects of temperature on the conductivity of the porcelains. ing mayhave a comparatively small efiect in improvingthe electrical resistanceat high temperatures once these properties have been deleterious'lyaffected by the lead deposits. The primary object of the presentinvention is a process of improving the electrical resistance propertiesof spark plug insulators that have been run on leaded gasolines.

In accordance with our invention after first cleaning the plugs, as bythe usual sand blasting or equivalent treatment, we treat the spark plugporcelains with a phosphoru compound or compounds. Phosphoric acid(H3PO4), phosphoric anhydride, alkyl phosphoric acids, organicphosphites and organic phosphates are typical examples of suitablephosphorus compounds.

The phosphorus compound is applied to the spark plug porcelain and thenthe spark plug is heated in any suitable manner as by heating in an ovenor by means of a torch to a tem-. perature on the order of about 700 to1000 degrees Fahrenheit to promote the desired reaction We have foundthat the sand blastspark plug run on leaded gasoline which had had notreatment. Curve B is a similar curve of a spark plug that was sandblasted only. Curves C and D illustrate the results obtained by sandwasheated to 1000 F. In curve D the spark plug porcelain had appliedthereto P205 and alcohol. The porcelain was thereafter heated to 700 F.Curve E illustrates values obtained from tests carried out on a newspark plug. The curves demonstrate that sand blasting by itself hadlittle beneficial effect and that the phosphorus treatments greatlyimproved the conductancetemperature relationships of the spark plugporcelains or insulators.

Measurements of spark plug resistances during actual operation in anengine have shown difierences inplug characteristics similar to thoserevealed by the conductance-temperature relationships determined undercontrolled temperaof the phosphorus compound or compounds with thedeposits in or on the spark plug porcelain. In the event anynon-volatile material collects in-the annular space about the porcelain;during the heating process, the plugs must be sand blasted a secondtime. The temperature-resistance relationships of the plugs as thusreconditioned are greatly improved.

The accompanying drawing forming a portion of this specificationcompares the effects of two difierent phosphorus treatments with theefiects of sand blasting alone on the electrical conductance vs.temperature relationships, as measured in an oven. The relationships ofa new unused plug and of a used plug which had no reconditioning areincluded for further comparison. In the figure, the values given forelectrical conductance represent the reciprocals of the resistance ofthe spark plug porcelains as measured in megohms. The temperatures areexpressed in degrees Fahrenheit. Curve A indicates the electricalconductance-temperature relationship of a ture condition in an oven.

The spark'plugs may also be reconditioned by installing the plug to betreated, after a preliminary sand blasting, in an engine and operatingthe engine at or near full loadon a gasoline containing up to about 0.3per cent of an organic phosphorus compound. It is desired to use no morethan about 0.3 per cent of the phosphorus compound to avoid excessivedeposits being I formed which might harm the movingengine parts.- Incase a leaded gasoline is used, it is de-' sirable to use trimethylphosphate since some phosphorus compounds depreciate the antiknockproperty of the tetraethyl lead; however, if a clear gasoline is used,any organic phosphorus compound'which is soluble in gasoline will havethe desired efiect.

As a specific example of results obtained from a spark plugreconditioned by being operated in an engine with a phosphorus compoundin the fuel, a plug which after preliminary sand blasting had 0.7megohm. of resistance under a given set of engine conditions, had .10megohms of resistance after burning 2 gallons of gasoline containing 10cc./ga1. of trimethyl phosphate. Under these same engine conditions,plugs which have resistances as low as 0.5 megohrn fail to fire theengine,

whereas new plugs operate steadily with 50 to megohms of resistance.

.Various changes and modlfications may be made in the specificprocedures outlined above without departing from the principles of ourinvention.

We claim: 7

l. A method of reconditioning a spark plug that has been operated onleaded gasoline which includes cleaning deposits from the spark plug andtreating the spark plug with a phosphorus compound.

2. A method of reconditioning a spark plug that has been operated on'leaded gasoline which includes sand blasting the spark plug, and thentreating the sand blasted plug with a phosphorus compound.

3. A method of reconditioning a spark plug 7. A method of reconditioninga spark plug that. has been operated on leaded gasoline which includessand blasting the spark plug and operating the plug in an engineemploying a leaded gasoline containing up to about 0.3% of trimethylphos- Dhate.

8. A method of reconditioning a spark plug that has been operated onleaded gasoline in order to improve the temperature-resistancecharacteristics thereof which includes, sand blasting said plug,treating the sand blasted plug with a phosphorus compound of the classof phosphorus compounds including phosphoric acid (H3PO4) phosphoricanhydride, alkyl phosphoric acids, organic phosphites and organicphosphates, and baking said plug at a temperature on the order of 700 to1000 degrees Fahrenheit.

9. A method of reconditioning a spark plug that has been operated onleaded gasoline which includes sand blasting the spark plug andoperating the sand blasted spark plug in an engine employing a gasolinecontaining up to about 0.3% of trimethyl phosphate.

ARTHUR S. FRY. LLOYD L. WITI-IROW.

